The present invention relates to a niobium powder which is suitable for producing capacitors, and to a process for producing niobium powder by the reduction of niobium oxides by means of alkaline earth metals and/or rare earth metals.
The reduction of heavy metal oxides by alkaline earth metals or hydrides is basically known; see U.S. Pat. No. 1,728,941, U.S. Pat. No. 2,516,863 and U.S. Pat. No. 4,687,632 for example. One problem is that the reduction proceeds strongly exothermically. After igniting a mixture of the oxide to be reduced and the reducing agent, the reaction proceeds substantially uncontrollably over a very short period of time, and the reaction mixture is heated to temperatures far in excess of 1000.degree. C. Reactions of this type can only be controlled with difficulty, due to the high pressure which builds up in the manner of an explosion, the need to dissipate the heat of reaction and the demands made on the reactor material. In particular, and among other problems, irreproducible grades of product with uncontrollable grain sizes are obtained. No success has hitherto been achieved in using this reaction for producing high purity acidic earth metal powders for use in capacitors.